1. Field of the Invention
The present invention relates to a coil component and its manufacturing method.
2. Description of the Related Art
A conventional coil component is manufactured by setting an air-core coil inside of a molding die, filling the molding die with mixed powders of magnetic powder and a binder or magnetic powder coated with a resin, and molding the coil component under pressure.
However, when the mixed powders of magnetic powder and a binder are used, it is difficult to uniformly mix the magnetic powder and the binder. As a result, it is difficult to obtain sufficient insulating properties in a resulting magnetic body, and accordingly, substantial current loss occurs. Furthermore, when the amount of the binder as compared to the magnetic powder is reduced in order to improve the magnetic characteristics of the coil component, the mixed powders of magnetic powder and a binder become non-uniform masses, and thus, it is difficult to fill the molding die with the mixed powders. Therefore, the density of the molded magnetic body is decreased, and thus, stable magnetic characteristics cannot be obtained and the mechanical strength is substantially reduced.
Furthermore, when a magnetic powder coated with only a resin is used, when the molding pressure is increased in order to reduce the space between magnetic particles, the resin breaks, and thus, sufficient insulating properties are not obtained in the magnetic body.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a coil component having excellent insulating properties and magnetic characteristics and greatly increased mechanical strength, and also provide a method of manufacturing such a novel a coil component.
According to a preferred embodiment of the present invention, a coil component includes a magnetic body made of magnetic powder, the surface of the magnetic powder is coated with at least two different types of resin layers, and a coil defined by a conductor having an insulating film provided thereon, at least a portion of which is embedded in the magnetic body. Here, a magnetic metal powder, for example, a pure iron powder, an amorphous powder, and a Sendust powder, is used for the magnetic powder.
Furthermore, a method for manufacturing a coil component according to another preferred embodiment of the present invention includes the steps of setting a coil component made of a conductor having an insulating film provided thereon in a mold, filling the mold with a magnetic powder, the surface of the magnetic powder being coated with at least two types of resin layers, pressing the magnetic powder to form a molded body in which the coil is embedded, and forming a magnetic body by heat-treating the molded body.
With the unique construction described above, even if the molding pressure is increased and heat-treatment is performed after the molding, breakdown of the inner resin layer is prevented and outstanding insulation between magnetic particles is achieved by using, for example, a thermosetting resin having a high mechanical strength for the inner resin layer. Moreover, the insulation between magnetic particles is further improved by providing an oxide film at the interface between the resin layer and the magnetic powder.
Further, by using, for example, a thermoplastic resin for the outer resin layer, the outer layer of the resin layers temporarily melts and then solidifies again when heat-treatment is performed after the molding, the bonding strength between magnetic particles greatly increases, and the space between magnetic particles is greatly reduced. As a result, the mechanical strength of the magnetic body is greatly increased.
Moreover, by using a thermosetting resin for the outer resin layer that is different from that of the inner resin layer, the outer resin layer that is not yet cured is completely cured by heat-treatment after the molding, the bonding strength between magnetic particles is greatly increased, and the space between magnetic particles is greatly reduced. As a result, the mechanical strength of the magnetic body is greatly increased.
Furthermore, the insulating properties and the mechanical strength of the magnetic body are greatly improved by providing a coating material made of either resin or glass on the surface of the magnetic body.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.